To increase the productivity of machines which process yarns, filaments and other elongated elements, it is possible, inter alia, to increase the yarn or filament travel speed of such machines. In the exemplary case of a spinning machine, this means an increase of the machine rotary speed. However, there are practical limits to the extent to which productivity can be boosted by boosting the rotary speed of the machine drive and accordingly the spindle speed. In particular, after a certain point, further increases in spindle rotary speed lead to yarn or filament breakages occurring at an unacceptably high frequency. Unacceptably high breakage frequencies are disadvantageous because, on the one hand, they decrease operating efficiency and, on the other hand, because they evidently have a negative effect upon the quality of the finished yarn, filament or other elongated element. For example, in the case of yarn being wound onto a cop, if the yarn breaks the partially filled cop is not replaced; instead, the broken yarn is tied, either manually or by means of an automatic knotter. Accordingly, the number of yarn breakages per unit time is directly reflected in the number of knots in the yarn per unit length and thus constitutes one elementary measure of quality.
Breakage of yarns, filaments or other elongated members in a function not only of the characteristics of the yarns of filaments, and of the processing operations to which they are subjected, including climatic conditions. Additionally, and in the exemplary case of a ring-traveller-type spinning machine, the yarn breakage frequency is dependent upon the mechanical and in general the physical characteristics of the machine and its operation, including those of the yarn-winding spindle and of the drawing mechanism. A further important cause of yarn breakage is high-frequency variation of the tensile load borne by the yarn (or other elongated element) attributable for the most part to imperfect mounting or geometry of the rotary and other components of the spinning mechanism.
Because of the many factors which contribute to breakages of yarns, filaments and other elongated elements, it is at best extremely difficult to determine the dominating cause or causes of high breakage frequency. For this reason, automatic intervention into the breakage-producing factors, which would be highly desirable, is scarcely possible. In this connection, it should be additionally noted that the causes which dominate may change with time, so that after a while different causes, for example temporary climatic conditions, may become the dominating causes of yarn breakage.
To the foregoing it should be added that in the past persons skilled in the art were limited to merely providing for the generation of optical or acoustic signals in response to yarn breakages.